Hello,

I have a 97 volvo 960 station wagon. Lately Ive noticed my gas mileage has been getting really bad. Than a couple of days ago my CEL came on. I went to go check it out and it came back with PO172 code and read Engine running too rich.

Called Autozone for pricing and was told that the O2 senor were about $95.

Should I replace them with the OEM or Bosch ones? And How hard is it to DIY? Any pictures of location would be great. And lastly will replacing the senor fix the problem or should I pay someone $100 to hook it up to a diagnostic machine.

Thanks

 

i had a simular problem with my 850. Gas milage dropping is a symptom of a bad 02 sensor. I got one from a salvage yard. It was hard getting it off and should have anti-seize on the threads when you put it back on. I have heard of people having problems getting the cel to reset when using after market sensors so I would try to get a oem one.

 

What makes you think the O2 is bad? Volvo OBDII holds the O2 to a pretty strict standard; it needn't deviate much before it will set a hard code and CEL. But, you mention you've been noticing the decreased mileage for a while? I'd focus on the engine coolant temp sensor. It has a much broader range of "acceptability" before it throws a code. It starts thinking it's 20 degrees outside and pumps the fuel!
The O2 may indeed be bad but think about this. The O2 is the last sensor in the system...the last information to be sent to the ecu. The last opportunity for the ecu to make corrections. Your mileage is down, the car's running rich....where did that information come from? The O2 sensor. Sounds to me like it's doing the job it's supposed to.
The ECT is on the very back of the head...kind of tough to get to, but loads cheaper than an O2 sensor.
Decreasing gas mileage is often accompanied by a bad O2 it's true. Frankly, without a digital multimeter and the specs, it's a guessing game. My experience with older Volvos is rather than one failed senso, it's often 2 or more that are borderline good. The combination of the low normal input causes crappy performance...similar to our federal legislators!!

 

Here is an update.

Since getting a reading on the check engine, the car now runs very rough and when I started and while in idle it shakes a lot. Can this be a misfiring problem.

Help me out guys, where should I start. I called a mechanic and told him about the error code and he told me it would cost $500 to fix.

Thanks

 

if the car is running really rough and shakey at idle, try unplugging the mass air flow sensor. It's on the air intake hose just past the air filter. If you unplug it and the engine smooths out it's faulty. Replace it, and if nothing else is too terribly out of whack hopefully all will be well.